title: Characterization of crocodile teeth: correlation of composition, microstructure, and hardness.
abstract: Structure and composition of teeth of the saltwater crocodile Crocodylus porosus were characterized by several high-resolution analytical techniques. X-ray diffraction in combination with elemental analysis and infrared spectroscopy showed that the mineral phase of the teeth is a carbonated calcium-deficient nanocrystalline hydroxyapatite in all three tooth-constituting tissues: Dentin, enamel, and cementum. The fluoride content in the three tissues is very low (<0.1 wt.%) and comparable to that in human teeth. The mineral content of dentin, enamel, and cementum as determined by thermogravimetry is 71.3, 80.5, and 66.8 wt.%, respectively. Synchrotron X-ray microtomography showed the internal structure and allowed to visualize the degree of mineralization in dentin, enamel, and cementum. Virtual sections through the tooth and scanning electron micrographs showed that the enamel layer is comparably thin (100-200 μm). The crystallites in the enamel are oriented perpendicularly to the tooth surface. At the dentin-enamel-junction, the packing density of crystallites decreases, and the crystallites do not display an ordered structure as in the enamel. The microhardness was 0.60±0.05 GPa for dentin, 3.15±0.15 GPa for enamel, 0.26±0.08 GPa for cementum close to the crown, and 0.31±0.04 GPa for cementum close to the root margin. This can be explained with the different degree of mineralization of the different tissue types and is comparable with human teeth.
authors.affiliation: Institute of Inorganic Chemistry and Center for Nanointegration Duisburg-Essen (CeNIDE), University of Duisburg-Essen, Universitaetsstr. 5-7, 45117 Essen, Germany.
authors.forename: Joachim
authors.initials: J
authors.lastname: Enax
authors.forename: Helge-Otto
authors.initials: HO
authors.lastname: Fabritius
authors.forename: Alexander
authors.initials: A
authors.lastname: Rack
authors.forename: Oleg
authors.initials: O
authors.lastname: Prymak
authors.forename: Dierk
authors.initials: D
authors.lastname: Raabe
authors.forename: Matthias
authors.initials: M
authors.lastname: Epple
mesh_terms: D000489:Alligators and Crocodiles; D000818:Animals; D003739:Dental Cementum / Q000737:chemistry / Q000000981:diagnostic imaging / Q000648:ultrastructure; D003743:Dental Enamel / Q000737:chemistry / Q000000981:diagnostic imaging / Q000648:ultrastructure; D003804:Dentin / Q000737:chemistry / Q000000981:diagnostic imaging / Q000648:ultrastructure; D017886:Durapatite / Q000737:chemistry; D006244:Hardness; D006801:Humans; D008903:Minerals / Q000737:chemistry; D013818:Thermogravimetry; D014070:Tooth / Q000737:chemistry* / Q000000981:diagnostic imaging; D014092:Tooth Root / Q000737:chemistry / Q000000981:diagnostic imaging / Q000648:ultrastructure; D014961:X-Ray Diffraction; D055114:X-Ray Microtomography
chemical_list: D008903:Minerals; D017886:Durapatite
keywords: Biomineralization; Calcium phosphate; Crocodiles; Mechanical properties; Synchrotron X-ray microtomography; Teeth